1. Field of the Invention
The present invention relates to a crane, and a crane assembling method.
2. Background Art
Heretofore, there has been known a crane which comprises: a boom; a luffing jib (hereinafter referred to simply as “jib”) attached to the boom in a raisable and lowerable manner; and a strut attached to the boom in a raisable and lowerable manner, to raise and lower the jib. This type of crane is disclosed, for example, in JP 2004-75294A, JP 4613897B and JP 04-033717B.
A method of attaching a jib to a boom includes an extending-type attaching method and an enfolding-type attaching method. In the extending-type attaching method, a jib is laid in front of a boom which is lowered and laid down, and, in this state, the jib is attached to the boom, as described, for example, in FIGS. 1 to 4 of the JP 2004-75294A. In the enfolding-type attaching method, a jib is laid under a boom which is lowered and laid down, and hoisted up, and, in this state, the jib is attached to the boom, as described, for example, in FIGS. 9 and 10 of the JP 4613897B. As compared to the enfolding-type attaching method, the extending-type attaching method facilitates assembling of a jib, although there is a need for a larger assembling space. As compared to the extending-type attaching method, the enfolding-type attaching method has more difficulty in performing an operation of attaching a jib to a boom. That is, in the enfolding-type attaching method, assemblability of a jib becomes poor. On the other hand, the enfolding-type attaching method needs less assembling space. Meanwhile, the enfolding-type attaching method includes an enfolding support-type attaching method described on FIGS. 3 to 7 of the JP 04-033717B, and a jib foot offset-type attaching method in which a jib foot is disposed at a position largely offset from a central axis of a boom.
A method of attaching a strut and a jib to a boom includes the following two processes. One is a process I in which the strut is attached to the boom, and then the jib is attached to the boom, and the other is a process II in which the jib is attached to the boom, and then the strut is attached to the boom. In the case where the process I is employed in the extending-type attaching method, an operation of attaching the jib to the boom has to be performed under the strut, so that assemblability of the jib becomes poor. In the case where the process I is employed in the enfolding-type attaching method, when the boom is positionally adjusted with respect to the jib placed on the ground (see, for example, FIG. 8 of the JP 4613897B), the boom has to be turned in a state in which the strut is attached thereto, so that it needs to take a long time for the position adjustment. As a result, assemblability of the jib becomes poor. On the other hand, in the case where the process II is employed in the extending-type attaching method, after attaching the jib to the boom, the strut is assembled above the jib, so that an assembling operation of the strut at a distal end of the boom has to be performed in high places, and thereby assemblability of the strut becomes poor. In the case where the process II is employed in the enfolding-type attaching method, a head of the boom cannot be placed in contact with the ground, so that the assembling operation of the strut at the distal end of the boom has to be performed in higher places, and thereby assemblability of the strut becomes poor.
As above, various methods have been employed in conventional cranes to attach a jib and a strut to a boom. However, each of the attaching methods has a problem with assemblability of the jib or strut.